Readily transmitting heat or thermal radiation; having the quality of being transparent or permeable to heat energy.
From Greek 'dia-' (through) + 'thermē' (heat) + '-anous' (adjective suffix), formed in 19th-century physics to describe materials' thermal properties.
Most plastics are more diathermanous than we realize—that's why plastic wrap creates that greenhouse effect and why leaving plastic bags in the sun can get the contents quite hot.
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